getsockopt and setsockopt

2020-09-12

了解一下 getsockopt 和 setsockopt

#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen);

参数：
sockfd: 必须是打开的套接字描述符;

level: 系统解释选项的代码或者是通用的套接字代码，或者是某个特定协议的代码(例如：IPv4、IPv6、TCP或者SCTP);

optname:选项名称

optval: 对于getsockopt()是讲选项当前值存放在 optval中，对于setsockopt()为系统设置新的选项值

optlen: 指定*optval的大小

结果：

函数执行成功返回0 出错返回-1

EBADF：sock不是有效的文件描述词
EFAULT：optval指向的内存并非有效的进程空间
EINVAL：在调用setsockopt()时，optlen无效
ENOPROTOOPT：指定的协议层不能识别选项
ENOTSOCK：sock描述的不是套接字

示例：

#include <arpa/inet.h>
#include <netdb.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/errno.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#define PORT 40501
#define MAXLINE 4096
// 读取n个字符
size_t readn(int fd, void *ptr, size_t maxcn) {
  size_t noreadcn, readcn;
  char *buf = (char *)ptr;
  noreadcn = maxcn;
  while (noreadcn > 0) {
    if ((readcn = read(fd, buf, noreadcn)) < 0) {
      if (errno == EINTR) {
        printf("中断错误");
        readcn = 0;
      } else {
        return -1;
      }
    } else if (readcn == 0)
      break;            // EOF
    noreadcn -= readcn; //读取的数据少于maxcn继续读
    buf += readcn;
    if (*buf == 0)
      break;
  }
  return (maxcn - noreadcn);
}
size_t writen(int fd, void *ptr, size_t maxcn) {
  size_t nowritecn, writecn;
  char *buf = (char *)ptr;
  nowritecn = maxcn;
  while (nowritecn > 0) {
    if ((writecn = write(fd, buf, nowritecn)) < 0) {
      if (errno == EINTR) {
        printf("中断错误");
        writecn = 0;
      } else {
        return -1;
      }
    } else if (writecn == 0)
      break;              // EOF
    nowritecn -= writecn; //写入的数据少于maxcn继续写
    buf += writecn;
    if (*buf == 0)
      break;
  }
  return (maxcn - nowritecn);
}

int main(int argc, char *argv[]) {
  int listenfd, Confd;
  fd_set rset, allset;
  struct sockaddr_in serverAddr, cliaddr;
  socklen_t clilen = sizeof(clilen);
  bzero(&serverAddr, sizeof(serverAddr));
  bzero(&cliaddr, clilen);
  listenfd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);

  int reuse = 1;
  if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, (int *)&reuse,
                 sizeof(int)) < 0) {
    printf("set socket fail");
    exit(-1);
  }

  serverAddr.sin_family = AF_INET;
  serverAddr.sin_port = htons(PORT);
  serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
  if (bind(listenfd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0) {
    perror("bind error");
    exit(-1);
  }
  listen(listenfd, 1024);
  while (true) {
    Confd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
    int opt;
    int optlen = sizeof(opt);
    if (getsockopt(listenfd, SOL_SOCKET, SO_KEEPALIVE, (int *)&opt, &optlen) <
        0) {
      printf("get sockopt fail");
      exit(-1);
    }
    printf(" keep-alive : %d\n", opt);
    const char *buf = "welcome to you";
    writen(Confd, (void *)buf, strlen(buf));
    shutdown(Confd, SHUT_RDWR);
  }
  return 0;
}